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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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NASA NTRS2014

Plasma and Energetic Particle Behaviors During Asymmetric Magnetic Reconnection at the Magnetopause

The factors controlling asymmetric reconnection and the role of the cold plasma population in the reconnection process are two outstanding questions. We present a case study of multipoint Cluster observations demonstrating that the separatrix and flow boundary angles are greater on the magnetosheath than on the magnetospheric side of the magnetopause, probably due to the stronger density than magnetic field asymmetry at this boundary. The motion of cold plasmaspheric ions entering the reconnection region differs from that of warmer magnetosheath and magnetospheric ions. In contrast to the warmer ions, which are probably accelerated by reconnection in the diffusion region near the subsolar magnetopause, the colder ions are simply entrained by 𝐄×𝐁 drifts at high latitudes on the recently reconnected magnetic field lines. This indicates that plasmaspheric ions can sometimes play only a very limited role in asymmetric reconnection, in contrast to previous simulation studies. Three cold ion populations (probably H+, He+, and O+) appear in the energy spectrum, consistent with ion acceleration to a common velocity.

Cluster↗
NASA NTRS1992

Analysis of cyclotron harmonic emissions at the outer planets

The flyby missions of Voyagers 1 and 2 at Jupiter, Saturn and Uranus revealed intense waves above the electron gyrofrequency. Observation of waves at the upper hybrid frequency is often accompanied by power at adjacent electron Bernstein harmonics, and the relative power in these modes depends both on the density and temperature ratios of the cold background electron population and the hot magnetospheric electrons which drive the instability. A model of electron distributions which is consistent with observations is used for analysis of the excited waves, their dependence upon plasma parameters, and the time scales of the saturation processes. It is shown that in the presence of two-temperature electron distributions the linear excitation is due to a fluidlike coupling of two eigenmodes for perpendicular propagation and to kinetic destalization of oblique modes. The dependence of linear growth rates on propagation angle is presented, along with results from particle simulations. A quasi-linear diffusion time for relaxing the hot electron loss cone is calculated and compared with simulation results. This time scale is faster than for local saturation by heating the cold population, and also the convective amplification time scale, suggesting that the waves saturate at quasi-linear levels, while being convectively localized to the equatorial regions of the outer planetary magnetospheres.

Roth, I.↗
NASA NTRS2003

Double Layers in Expanding Plasmas and Their Relevance to the Auroral Plasma Processes

When a dense plasma consisting of a cold and a sufficiently warm electron population expands, a rarefaction shock forms [Bezzerides et al., 1978]. In the expansion of the polar wind in the magnetosphere, it has been previously shown that when a sufficiently warm electron population also exists, in addition to the usual cold ionospheric one, a discontinuity forms in the electrostatic potential distribution along the magnetic field lines [Barakat and Schunk, 1984]. Despite the lack of spatial resolution and the assumption of quasi-neutrality in the polar wind models, such discontinuities have been called double layers (DLs). Recently similar discontinuities have been invoked to partly explain the auroral acceleration of electrons and ions in the upward current region [Ergun et al., 2000]. By means of one-dimensional Vlasov simulations of expanding plasmas, for the first time we make here the connection between (1) the rarefaction shocks, (2) the discontinuities in the potential distributions, and (3) DLs. We show that when plasmas expand from opposite directions into a deep density cavity with a potential drop across it and when the plasma on the high-potential side contains hot and cold electron populations, the temporal evolution of the potential and the plasma distribution generates evolving multiple double layers with an ,extended density cavity between them. One of the DLs is the rarefaction-shock (RFS) and it forms by the reflections of the cold electrons coming from the high-potential side; it supports a part of the potential drop approximately determined by the hot electron temperature. The other DLs evolve from charge separations arising either from reflection of ions coming from the low-potential side or stemming from plasma instabilities; they support the rest of the potential drop. The instabilities forming these additional double layers involve electron-ion (e-i) Buneman or ion-ion (i-i) two-stream interactions. The electron-electron two-stream interactions on the high-potential side of the RFS generate electron-acoustic waves, which evolve into electron phase-space holes. The ion population originating from the low-potential side and trapped by the RFS is energized by the e-i and i-i instabilities and it eventually precipitates into the high-potential plasma along with an electron beam. Applications of these findings to the auroral plasma physics are discussed.

Singh, Nagendra↗
NASA NTRS1989

Plasma and energetic electron flux variations in the Mercury 1 C event - Evidence for a magnetospheric boundary layer

Charge-particle and magnetic-field data obtained during the first encounter (on March 29, 1974) of Mariner 10 with the planet Mercury are reexamined, and a new interpretation of the Mariner 10 energetic electron, plasma electron, and magnetic field data near the outbound magnetopause at Mercury is presented. It is shown that Mariner 10 sampled the hot substorm energized magnetospheric plasma sheet for the first 36 sec of the C event and, for the next 48 sec, alternatively sampled hot (plasma sheet) and cold (boundary-layer magnetosheathlike) plasma regions. It is argued that the counting rate of the ID1 event (i.e., a particle event triggering detector D1 but not the D2, D3, or D7 detectors) throughout the C event most probably represents a pulse pileup response to about 35-175 keV electrons, rather than the nominal above-175 keV electrons presumed in the earlier interpretations.

Christon, S. P.↗
NASA NTRS1986

Interactions of planetary magnetospheres with icy satellite surfaces

When natural satellites and ring particles are embedded within magnetospheric plasmas, the charged particles interact with the surfaces of these solid bodies. These interactions have important implications for the surface, the atmosphere of the parent body, and the magnetosphere as a whole. Significant erosion of the surface by sputtering, as well as redeposition of sputter ejecta, can occur over geologic time. The surface can also be chemically modified. Sputter ejecta can make important contributions to the atmosphere; sputtering provides a lower limit to the atmospheric column density even for arbitrarily cold satellite surfaces. Sputter ejecta escaping from the parent body can form extensive neutral clouds within the magnetosphere. Ionization and dissociation within these neutral clouds can be dominant sources of low-energy plasma. The importance of these processes is discussed for the satellites and magnetospheres of Jupiter, Saturn and Uranus.

Cheng, A. F.↗
NASA NTRS2000

TIDE Observations of Cusp and Cleft Multiple Ion Populations

The southern pole pass of Polar/TIDe at 5000 km allows a study of the distributions of the cusp and cleft. We discuss observations of TIDE (Thermal Ion Dynamics Experiment) as it passes the southern pole on March 29, 1999. A mixture of several cold outflowing ions (0.3-10 eV) are measured simultaneously with magnetospheric precipitation (greater than 100 eV). We will show a study of these multiple plasma distributions, their source, and their interaction.

Coffey, Victoria N.↗
NASA NTRS1973

Jupiter's outer atmosphere.

The current state of the theory of Jupiter's outer atmosphere is briefly reviewed. The similarities and dissimilarities between the terrestrial and Jovian upper atmospheres are discussed, including the interaction of the solar wind with the planetary magnetic fields. Estimates of Jovian parameters are given, including magnetosphere and auroral zone sizes, ionospheric conductivity, energy inputs, and solar wind parameters at Jupiter. The influence of the large centrifugal force on the cold plasma distribution is considered. The Jovian Van Allen belt is attributed to solar wind particles diffused in toward the planet by dynamo electric fields from ionospheric neutral winds, and the consequences of this theory are indicated.

Brice, N. M.↗
NASA NTRS1989

Acceleration of thermal plasma in the magnetosphere

Analytic theory and numerical simulations are used here to investigate the physics of two types of mixed plasmas. The transverse acceleration of ions on auroral field lines is considered in order to determine the effects of multiion species. In the auroral zone the components of a multiion plasma, including hydrogen and oxygen, interact with each other as well as with a two-component electron plasma composed of both a magnetospheric beam and background ionospheric components. This interaction occurs as a mixed ion-ion hybrid mode. How an electron plasma, with both hot and cold components as well as ion beams, affects the plasma sheet boundary layer is examined. It is found that in the presence of this mixed electron plasma, warm ion beams can drive the electron acoustic instability; this phenomenon may be responsible for broadband electrostatic noise in the boundary layer.

Ashour-Abdalla, Maha↗
NASA NTRS2007

Observations of a Newly "Captured" Magnetosheath Field Line: Evidence for "Double Reconnection"

We have begun an investigation of the nature of the low-latitude boundary layer in the mid-altitude cusp region using data from the Polar spacecraft. This region has been routinely sampled for about three months each year for the periods 1999-2001 and 2004-2006. The low-to-mid-energy ion instruments frequently observed dense, magnetosheath-like plasma deep (in terms of distance from the magnetopause and in invariant latitude) in the magnetosphere. One such case, taken during a period of northward interplanetary magnetic field (IMF), shows magnetosheath ions within the magnetosphere with velocity distributions resulting from two separate merging sites along the same field lines. Cold ionospheric ions were also observed counterstreaming along the field lines, evidence that these field lines were closed. These results are consistent with the hypothesis that double merging can produce closed field .lines populated by solar wind plasma. Through the use of individual cases such as this and statistical studies of a broader database we seek to understand the morphology of the LLBL as it projects from the sub-solar region into the cusp. We will present preliminary results of our ongoing study.

Chandler, Michael O.↗
NASA NTRS2007

Recent Plasma Observations Related to Dayside Magnetic Merging and the Low-latitude Boundary Layer

We have begun an investigation of the nature of the low-latitude boundary layer in the mid-altitude cusp region using data from the Polar spacecraft. This region has been routinely sampled for about three months each year for the periods 1999-2001 and 2004-2006. The low-to-mid-energy ion instruments frequently observed dense, magnetosheath-like plasma deep (in terms of distance from the magnetopause and in invariant latitude) in the magnetosphere. One such case, taken during a period of northward interplanetary magnetic field (IMF), shows magnetosheath ions within the magnetosphere with velocity distributions resulting from two separate merging sites along the same field lines. Cold ionospheric ions were also observed counterstreaming along the field lines, evidence that these field lines were closed. These results are consistent with the hypothesis that double merging can produce closed field lines populated by solar wind plasma. Through the use of individual cases such as this and statistical studies of a broader database we seek to understand the morphology of the LLBL as it projects from the sub-solar region into the cusp. We will present preliminary results of our ongoing study.

Chandler, Michael O.↗
NASA NTRS1983

Corotation anisotropies in Saturn's magnetosphere

Ion data from the Voyager 1 and 2 low-energy charged particle (LECP) experiment are fit to a second-order harmonic expansion to determine anisotropies within the Saturnian magnetosphere. Anisotropies from the low-energy channels (28-130 keV) are often consistent with those expected from corotation (generally with a small radial component on the dayside) but are at times distinctly different from corotation. On the dayside, near the noon meridian, first-order anisotropies often depart significantly from the corotation direction. On the nightside, amplitudes are consistent with full corotation but begin to drop below corotation values at a dipole L of approximately 27 Saturn radii (corresponding to a velocity of approximately 265 km/s). Second-order anisotropies are significant, even dominant at times, on the dayside where a relatively broad range of pitch angles is sampled by the instrument. In all cases there is a departure of approximately 180 deg from the first-order anisotropies expected due to corotation beginning outside the Rhea L shell and continuing through at least the orbit of Dione. This is the region where the cold and hot plasma tori have been observed. The anisotropies expected from rigid corotation of the observed flux distributions are computed, and it is concluded that parts of the Saturnian magnetosphere are not rigidly corotating. Calculations based on the combined effects of corotation plus solar wind generated convective electric fields appear to provide insights into the anisotropies along the dawn meridian. However, on the dayside near noon, turbulence and/or time variations seem necessary to explain the departure from simple convection models.

Carbary, J. F.↗
NASA NTRS1985

Structure of the plasmapause from ISEE 1 low-energy ion and plasma wave observations

Low-energy ion pitch angle distributions are compared with plasma density profiles in the near-earth magnetosphere using ISEE 1 observations. The classical plasmapause determined by the sharp density gradient is not always observed in the dayside region, whereas there almost always exists the ion pitch angle distribution transition from cold, isotropic to warm, bidirectional, field-aligned distributions. In the nightside region the plasmapause density gradient is typically found, and it normally coincides with the ion pitch angle distribution transition. The sunward motion of the plasma is found in the outer part of the 'plasmaspheric' plasma in the dusk bulge region.

Nagai, T.↗
NASA NTRS1973

High-frequency electrostatic waves in the magnetosphere.

High-frequency electrostatic microinstabilities in magnetospheric plasmas are considered in detail. Rather special plasma parameters are found to be required to match the theoretical wave spectrum with satellite observations in the magnetosphere. In particular, it is necessary to have a cold and a warm species of electrons such that (1) the warm component has an anomalous velocity distribution function that is nonmonotonic in the perpendicular component of velocity and is the source of free energy driving the instabilities, (2) the density ratio of the cold component to the hot component is greater than about 0.01, and (3) the temperature ratio of the two components for cases of high particle density is no less than 0.1. These requirements and the corresponding instability criteria are satisfied only in the trapping region; this is also the region in which the waves are most frequently observed. The range of unstable wavelengths and an estimate of the diffusion coefficient are also obtained. The wave are found to induce strong diffusion in velocity space for low-energy electrons during periods of moderate wave amplitude.

Young, T. S. T.↗
NASA NTRS1977

Electrostatic emissions between electron gyroharmonics in the outer magnetosphere

A scheme was constructed and a theoretical model was developed to classify electrostatic emissions. All of the emissions appear to be generated by the same basic mechanism: an unstable electron plasma distribution consisting of cold electrons (less than 100 eV) and hot loss cone electrons (about 1 keV). Each emission class is associated with a particular range of model parameters; the wide band electric field data can thus be used to infer the density and temperature of the cold plasma component. The model predicts that gyroharmonic emissions near the plasma frequency require large cold plasma densities.

Hubbard, R. F.↗
NASA NTRS1990

Perpendicular heating of electrons by upper hybrid waves generated by a ring distribution

Satellite observations of electron conical distributions with enhanced fluxes just outside the loss cone suggest that telectrons have been heated perpendicularly to the magnetic field in the mid-altitude polar magnetosphere. To understand electron conical distributions, plasma simulations are conducted to examine an upper hybrid wave instability of a ring electron distribution perpendicular to the magnetic field in a cold electron background. The simulations indicate that both the cold and ring distributions are heated perpendicularly during the saturation stage. From the plasma data, a ring distribution can be identified as a trapped distribution function with an enhancement near 90-deg pitch angle in the phase space density plot. It is suggested that the ring distribution might provide an additional free energy source for generating upper hybrid waves associated with electron conical events.

Lin, C. S.↗
NASA NTRS1992

Electron acceleration by Alfven waves in the magnetosphere

The self-consistent electron kinetics of Alfven waves on the electron inertial scale is studied using a 2D hybrid-kinetic description. The ions follow a fluid description for Alfven waves at frequencies below the ion cyclotron frequency. The parallel electron dynamics is treated kinetically using particle-in-cell techniques. In this model, the electron plasma mode is eliminated, and only the physics of the Alfven waves is retained. At sufficiently large amplitudes, it is found that oblique Alfven waves break due to finite electron inertia in a cold plasma. The consequence of wave breaking is the formation of an electron beam which can be unstable to the beam-plasma instability. The electrons supporting the parallel current thermalize into a non-Maxwellian distribution with an energetic tail up to several keV, assuming a reasonable magnetospheric Alfven speed. In hot plasma simulations, electron trapping is the principal mechanism of electron acceleration. It is proposed that wave breaking or electron trapping of oblique Alfven waves at 1 R(E) can result in electron acceleration and may explain some observed auroral phenomena.

Hui, C.-H.↗
NASA NTRS1999

Investigations of Remote Plasma Irregularites by Radio Sounding: Applications of the Radio Plasma Imager on IMAGE

The Radio Plasma Imager (RPI) on the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) mission operates like a radar by transmitting and receiving coherent electromagnetic pulses. Long-range echoes of electromagnetic sounder waves are reflected at remote plasma cutoffs. Thus, analyses of RPI observations will yield the plasma parameters and distances to the remote reflection points. These analyses assume that the reflecting plasma surfaces are cold and are sufficiently smooth that they effectively behave as plane mirrors to the incoming sounder waves, i.e., that geometric optics can be used. The RPI will employ pulse compression and spectral integration techniques, perfected in ground-based ionospheric digital sounders, in order to enhance the signal-to-noise ratio in long-range magnetospheric sounding. When plasma irregularities exist in the remote magnetospheric plasmas that are being probed by the sounder waves, echo signatures may become complicated. Ionospheric sounding experience indicates that while topside sounding echo strengths can actually be enhanced by the presence of irregularities, ground-based sounding indicates that coherent detection techniques can still be employed. In this paper we investigate the plasma conditions that will allow coherent signals to be detected by the RPI and the signatures to be expected, such as scattering and plasma resonances, in the presence of multi-scale irregularities, may possibly have on RPI signals. Sounding of irregular plasma structures in the plasmasphere, plasmapause and magnetopause are also discussed.

Fung, Shing F.↗
NASA NTRS2013

Plasma Ion Composition Measurements for Europa

Jupiter magnetospheric interactions and surface composition, both important to subsurface ocean detection for the Galilean icy moons Europa, Ganymede, and Callisto, can be measured using plasma ion mass spectrometry on either an orbiting spacecraft or one designed for multiple flybys of these moons. Detection of emergent oceanic materials at the Europa surface is more likely than at Ganymede and Callisto. A key challenge is to resolve potential intrinsic Europan materials from the space weathering patina of iogenic species implanted onto the sensible surface by magnetospheric interactions. Species resolved measurements of pickup ion currents are also critical to extraction of oceanic induced magnetic fields from magnetospheric interaction background dominated by these currents. In general the chemical astrobiological potential of Europa should be determined through the combination of surface, ionospheric, and pickup ion composition measurements. The requisite Ion Mass Spectrometer (IMS) for these measurements would need to work in the high radiation environment of Jupiter's magnetosphere between the orbits of Europa and Ganymede, and beyond. A 3D hybrid model of the moon magnetosphere interaction is also needed to construct a global model of the electric and magnetic fields, and the plasma environment, around Europa. Europa's ionosphere is probably usually dominated by hot pickup ions with 100-1000 eV temperatures, excursions to a "classical" cold ionosphere likely being infrequent. A field aligned ionospheric wind driven by the electron polarization electric field should arise and be measurable.

Plasma↗